Image forming apparatus

ABSTRACT

An image forming apparatus includes: an image carrying unit that carries an image to be transferred to a sheet which is brought into contact with the image carrying unit and passed through; a separation unit that separates the sheet from the image carrying unit; and a removal unit that comes into contact with the image carrying unit, and removes toner remaining after the sheet passes through the separation unit. A non-transferred toner image that is not transferred to the sheet is formed in a range, where the separation unit is not present, of the image carrying unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2019-161665 filed on Sep. 5, 2019.

BACKGROUND (i) Technical Field

The present disclosure relates to an image forming apparatus.

(ii) Related Art

What is disclosed in Japanese Patent No. 4687642 and Japanese UnexaminedPatent Application Publication No. 11-219035 is known as conventionaltechniques that cope with a problem which may occur due to a separationunit that separates a sheet of paper from an image carrying unit such asa photoreceptor.

Japanese Patent No. 4687642 describes an image forming apparatusincluding a separation unit that separates a recording medium from thesurface of a photoreceptor drum and guides the recording medium in atransport direction. The separation unit includes a separation claw incontact with the photoreceptor drum, and an auxiliary claw disposed onboth sides of the separation claw and not in contact with thephotoreceptor drum. The auxiliary claw guides the transport of therecording medium separated by the separation claw so that the recordingmedium does not come into contact with the back of the separation claw,and the auxiliary claw is fitted from the above after the separationclaw is mounted to a mounting position.

Japanese Unexamined Patent Application Publication No. 11-219035describes a separation device of an image forming apparatus in which atoner image formed on the surface of an image carrier is transferred toa sheet of paper, and part of a claw-like separation member is broughtinto contact with the surface of the image carrier to separate the sheetabsorbed in the surface of the image carrier, where the separationdevice has a shape which allows the separation device to pass through acontact portion between the claw-like separation member and the imagecarrier. Japanese Unexamined Patent Application Publication No.11-219035 describes that the part of the claw-like separation member isbrought into contact with the surface of the image carrier with a widthin an axial direction, and an introduction surface is formed on theleading end side of the contact portion between the separation memberand the image carrier, the introduction surface being configured toallow remaining toner adhering on the image carrier to pass through thecontact portion without being blocked by the contact portion.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate toan image forming apparatus that can reduce adherence of part of thetoner in a non-transferred toner image formed in an image carrying unitto a portion, where a sheet of paper passes through, of a separationunit that separates a sheet of paper from the image carrying unit, ascompared with when the non-transferred toner image is similarly formedin a range of the image carrying unit, where the separation unit ispresent.

Aspects of certain non-limiting embodiments of the present disclosureaddress the above advantages and/or other advantages not describedabove. However, aspects of the non-limiting embodiments are not requiredto address the advantages described above, and aspects of thenon-limiting embodiments of the present disclosure may not addressadvantages described above.

According to an aspect of the present disclosure, there is provided animage forming apparatus including an image carrying unit that carries animage to be transferred to a sheet which is brought into contact withthe image carrying unit and passed through; a separation unit thatseparates the sheet from the image carrying unit; and a removal unitthat comes into contact with the image carrying unit, and removes tonerremaining after the sheet passes through the separation unit. Anon-transferred toner image that is not transferred to the sheet isformed in a range, where the separation unit is not present, of theimage carrying unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic view illustrating the entirety of an image formingapparatus according to a first exemplary embodiment;

FIG. 2 is a schematic view illustrating part of the image formingapparatus of FIG. 1;

FIG. 3 is a schematic perspective view illustrating another part of theimage forming apparatus of FIG. 1;

FIG. 4 is a block diagram illustrating the configuration of a controlunit in the image forming apparatus of FIG. 1;

FIG. 5 is a schematic view illustrating the configuration of ranges inthe outer circumferential surface of an intermediate transfer belt;

FIG. 6 is a conceptual view illustrating the configuration of the rangeof the intermediate transfer belt, where a separation unit is notpresent;

FIG. 7 is a schematic view illustrating the range where anon-transferred toner image is formed;

FIG. 8 is a schematic view illustrating the states of the rear end of asheet of paper and a separation unit;

FIG. 9 is a schematic view illustrating part of an image formingapparatus according to a second exemplary embodiment;

FIG. 10 is a schematic view illustrating another configuration exampleof times when a low concentration non-transferred toner image is formedin the image forming apparatus of FIG. 9;

FIG. 11 is a graph illustrating a result of an experiment to investigatethe relationship between the concentration of a low concentrationnon-transferred toner image and occurrence of stain at the rear end of asheet of paper;

FIG. 12 is a schematic view illustrating part of an image formingapparatus according to a third exemplary embodiment;

FIG. 13A is a perspective view illustrating a separation device in theimage forming apparatus of FIG. 12, and FIG. 13B is a perspective viewillustrating a state where the separation device is disassembled;

FIG. 14 is a schematic view illustrating the states of the separationdevice of FIGS. 13A and 13B, and the rear end of a sheet of paper;

FIG. 15 is a schematic view illustrating a comparative example relatedto the range where a non-transferred toner image is formed;

FIG. 16A is a schematic view illustrating an example of state when thenon-transferred toner image illustrated in FIG. 15 is formed, and FIG.16B is a schematic view illustrating an example of state where the rearend of a sheet of paper comes contact with the separation device in thecase of FIG. 16A; and

FIG. 17 is a schematic view illustrating an example of state when stainat the rear end of a sheet of paper is noticeable.

DETAILED DESCRIPTION

Hereinafter exemplary embodiments of the disclosure will be describedwith reference to the drawings.

First Exemplary Embodiment

FIGS. 1 and 2 illustrate an image forming apparatus 1 according to afirst exemplary embodiment. FIG. 1 illustrates the entire configurationof the image forming apparatus 1, and FIG. 2 illustrates part(primarily, the second transfer position and its surrounding area) ofthe configuration of the image forming apparatus 1.

The arrows labeled with the symbols X, Y, Z in the drawings such as FIG.1, FIG. 2 indicate the directions of width, height, and depth ofthree-dimensional space defined in the drawings. In each of thedrawings, a circle symbol at the intersection of the arrows in the X andY directions indicates that the Z direction is toward the verticaldownward of the drawing surface.

The image forming apparatus 1 is an apparatus that forms an imagecomposed of toner as a developer on a sheet of paper 9 which is anexample of a recording medium. The image forming apparatus 1 in thefirst exemplary embodiment is implemented as a printer that forms animage corresponding to image information inputted from an externalconnection device such as an information terminal device, for instance.

As illustrated in FIG. 1, in the internal space of a housing 10, theimage forming apparatus 1 includes an image forming device 2 that formsa toner image based on image information; an intermediate transferdevice 3 that temporarily holds the image formed by the image formingdevice 2 then secondarily transfers the image to the sheet of paper 9; asheet feeding device 4 that stores and supplies sheets of paper 9 to besupplied to the position at which secondary transfer is performed by theintermediate transfer device 3; a fixing device 5 that fixes a tonerimage secondarily transferred by the intermediate transfer device 3 tothe sheet of paper 9; and a control unit 15 that performs controlrelated to the operations of the devices mentioned above.

The image information is information on an image such as a character, afigure, a photograph, and a pattern, for instance. The housing 10 is astructure formed in a desired shape with various support members andexterior materials. Part of the upper surface of the housing 10 includesa discharge storage 12 that stores sheets of paper 9 in a stacked state,which are discharged after an image is formed; and a discharge port 13through which the sheet of paper 9 is discharged to the dischargestorage 12. The dashed-dotted line of FIG. 1 and other figures indicatesa primary transport path when the sheet of paper 9 is transported withinthe housing 10.

The image forming device 2 includes four image forming devices 2Y, 2M,2C, and 2K that exclusively form toner images of four colors: yellow(Y), magenta (M), cyan (C), and black (K), respectively.

Each of the four image forming devices 2 (Y, M, C, K) has aphotoreceptor drum 21 which is an example of an image carrying unit thatrotates in the direction indicated by an arrow A, and the image formingdevice 2 is formed by disposing devices, such as a charging device 22,an exposure device 23, a developing device 24 (Y, M, C, K), a firsttransfer device 25, and a drum cleaning device 26, in the surroundingsof each photoreceptor drum 21. In FIG. 1, all of the symbols 21 to 26are labeled to the image forming device 2K for black (K) only, and partof the symbols are labeled to the image forming devices (Y, M, C) forother colors.

Among all, the charging device 22 is a device that charges the outercircumferential surface (surface allowing formation of an image) of thephotoreceptor drum 21 to a desired surface potential. The exposuredevice 23 is a device that performs light exposure on the outercircumferential surface of the photoreceptor drum 21 based on imageinformation, and forms an electrostatic latent image having desiredcolor components (Y, M, C, K). The developing device 24 (Y, M, C, K) isa device that develops the electrostatic latent image formed on theouter circumferential surface of the photoreceptor drum 21 withdeveloper (toner) corresponding desired colors (Y, M, C, K), and forms atoner image. The first transfer device 25 is a device thatelectrostatically transfers the toner image of each color to theintermediate transfer device 3 (an intermediate transfer belt 31). Thedrum cleaning device 26 is an example of a removal unit that scrapes andremoves unnecessary toner and unwanted substances, such as paper powder,adhering to the outer circumferential surface of the photoreceptor drum21 to clean the outer circumferential surface of the photoreceptor drum21.

In these image forming devices 2 (Y, M, C, K), each location where thephotoreceptor drum 21 and the first transfer device 25 are opposed toeach other is the first transfer position at which the first transfer ofa toner image is performed.

The intermediate transfer device 3 is a device configured to carry atoner image of each color formed by the image forming devices 2 (Y, M,C, K) by the first transfer, then transport the toner image to aposition at which the second transfer is performed on the sheet of paper9. The intermediate transfer device 3 is disposed on the upper side ofthe image forming devices 2 (Y, M, C, K) within the housing 10, andspecifically includes an intermediate transfer belt 31 which is anotherexample of the image carrying unit to which a toner image is firsttransferred from each photoreceptor drum 21 of the image forming devices2 (Y, M, C, K), and which carries the toner image. The intermediatetransfer device 3 is formed by disposing the following devices in thesurroundings of the intermediate transfer belt 31.

The intermediate transfer belt 31 is supported by multiple supportrollers 32 a to 32 e disposed therewithin so as to pass through thefirst transfer positions of the image forming devices 2 (Y, M, C, K)sequentially and rotate (circumferential movement) in the directionindicated by an arrow B.

The support roller 32 a of the multiple support rollers 32 a to 32 e isformed as a drive roller and a second transfer backup roller, and thesupport roller 32 b is formed as a tension roller. The support rollers32 c, 32 d are formed as surface rollers that holds the belt position(surface) when the first transfer positions of the intermediate transferbelt 31 are passed, and the support roller 32 e is formed as a cleaningbackup roller of the later-described belt cleaning device (36). Thesupport roller 32 e is formed as a cleaning backup roller for thelater-described belt cleaning device 36.

The support rollers 32 a to 32 e are rotatably provided in a supportframe (not illustrated) of the intermediate transfer device 3.

The first transfer device 25 of each of the image forming devices 2 (Y,M, C, K) is disposed inwardly of the intermediate transfer device 3. Thefirst transfer device 25 is included as part of the intermediatetransfer device 3, and the intermediate transfer belt 31 is pressedagainst the photoreceptor drum 21 by a first transfer member, in a rollform or the like, to which a first transfer current is supplied.

A second transfer device 35 is disposed at the outer circumferentialsurface portion supported by the support roller 32 a of the intermediatetransfer belt 31. The second transfer device 35 allows the sheet ofpaper 9 to pass through and secondarily transfers a toner image on theintermediate transfer belt 31 to the sheet of paper 9. The secondtransfer device 35 is configured to allow the sheet of paper 9 to betransported in contact with and pressed against the outercircumferential surface portion of the intermediate transfer belt 31 bya second transfer member, in a roll form or the like, to which a secondtransfer current is supplied, the outer circumferential surface portionbeing supported by the support roller 32 a.

In the intermediate transfer device 3, the location where the outercircumferential surface of the intermediate transfer belt 31 is incontact with the second transfer device 35 is a second transfer positionTP2 at which the second transfer of a toner image is performed.

In the surroundings of the outer side of the intermediate transfer belt31, a belt cleaning device 36 is disposed, which is another example of aremoval unit that removes unwanted substances such as unnecessary toneradhering to the outer circumferential surface of the intermediatetransfer belt 31 to clean the outer circumferential surface of theintermediate transfer belt 31.

The belt cleaning device 36 is formed by disposing inside a housing 36a, a plate-like cleaning member 36 b that removes unwanted substances bybeing in contact with the outer circumferential surface of the portionsupported by the roller 32 e of the intermediate transfer belt 31, and acollecting member 36 c that rotates and collects the unwanted substancesremoved by the cleaning member 36 b. In the belt cleaning device 36, asillustrated in FIGS. 1 and 5, the cleaning member 36 b is disposed in arotational direction B of the intermediate transfer belt 31 so as to bein contact with the intermediate transfer belt 31 in a width direction(or an axial direction) J substantially perpendicular to the rotationaldirection B of the intermediate transfer belt 31 at a position on thepath from the support roller 32 a to the support roller 32 b.

In addition, in the surroundings of the outer side of the intermediatetransfer belt 31, a separation device 37 is disposed, which is anexample of a separation unit that separates the sheet of paper 9 afterthe second transfer from the outer circumferential surface of theintermediate transfer belt 31.

As illustrated in FIG. 3, the separation device 37 is disposed as twoseparation devices 37A, 37B with a desired interval in the widthdirection J of the intermediate transfer belt 31. As illustrated in FIG.3, each of the separation devices 37A, 37B includes a separation claw371 having a tapered leading end, mounted on a fixing frame 370 as asupport unit swingably in the directions indicated by arrows D1, D2 witha support shaft 372 serving as a fulcrum; and an elastic member 373,such as a coil spring, which urges the separation claw 371 in thedirection indicated by the arrow D1 so that a leading end 371 a of theseparation claw 371 elastically comes into contact with the outercircumferential surface of the intermediate transfer belt 31. Asillustrated in FIG. 3, these two separation devices 37A, 37B are mountedso as to be disposed at predetermined positions of a mounting plate 38.The mounting plate 38 is fixed to, for instance, a support frame (notillustrated) of the intermediate transfer device 3.

The sheet feeding device 4 is a device configured to store and supplythe sheets of paper 9 to be supplied to the second transfer position TP2of the intermediate transfer device 3. The sheet feeding device 4 isdisposed at a position on the lower side of the image forming devices 2(Y, M, C, K) inside the housing 10, and is formed by disposingspecifically devices such as a storage body 41 of sheets of paper, and afeeding device 43.

The storage body 41 is a storage member having a stacking plate 42 forstoring multiple sheets of paper 9 stacked in a desired orientation, andis mounted to allow an operation such as drawing the storage member tothe outside of the housing 10 and loading the sheets of paper 9. Thefeeding device 43 is a device that delivers the uppermost one of thesheets of paper 9 stacked on the stacking plate 42 of the storage body41 one by one by sheet delivery devices such as multiple rollers. Thesheet of paper 9 may be a recording medium, such as regular paper,coated paper, or thick paper, which can be transported within thehousing 10 of the image forming apparatus 1, and allows transfer andfixing of a toner image, and the quality and form of the recordingmedium is not particularly restricted.

The fixing device 5 is a device configured to fix a toner image to thesheet of paper 9, the toner image being secondarily transferred by theintermediate transfer device 3. The fixing device 5 is disposed at aposition on the upper side of the second transfer position TP2 of theintermediate transfer device 3 within the housing 10, and is formed bydisposing specifically devices, such as a rotational body 51 forheating, and a rotational body 52 for pressurizing, in the internalspace of the housing 10 provided with an introduction port and adischarge port for the sheets of paper 9.

The rotational body 51 for heating is a rotational body in a roll formor a belt-pad form rotatable in the direction indicated by an arrow, andis heated so that the outer circumferential surface is maintained at adesired temperature by a heating unit which is not illustrated. Therotational body 52 for pressurizing is a rotational body in a roll formor a belt-pad form, which comes into contact with the rotational body 51to be driven and rotate under a desired pressure. The rotational body 52for pressurizing may be heated by a heating unit.

In the fixing device 5, the location where the rotational body 51 forheating and the rotational body 52 for pressurizing are in contact witheach other serves as a nip part (fixing processor) FN that performsprocessing such as heating, pressurizing for fixing an unfixed tonerimage to the sheet of paper 9.

In the image forming apparatus 1, as illustrated in FIG. 1, a sheetfeeding transport path Rt1 for transporting and supplying the sheet ofpaper 9 at the sheet feeding device 4 to the second transfer positionTP2 is provided between the sheet feeding device 4 and the secondtransfer position TP2 of the intermediate transfer device 3. Asillustrated in FIGS. 1 and 2, the sheet feeding transport path Rt1 isformed by disposing a pair of transport rollers 44 that sandwich andtransport the sheet of paper 9, and multiple guiding members 45 a, 45 bthat ensure the transport space for the sheet of paper 9 and guide thetransport of the sheet of paper 9. Among these, the transport rollers 44are formed as delivery rollers, so-called registration rollers thatcorrect skew of the sheet of paper 9 and deliver the sheet of paper 9 ata desired timing synchronized with the second transfer.

In the image forming apparatus 1, as illustrated in FIGS. 1 and 2, anintroduction transport path Rt2 is provided between the second transferposition TP2 of the intermediate transfer device 3 and the nip part FNof the fixing device 5 for introducing the sheet of paper 9 after thesecond transfer to the nip part FN. As illustrated in FIG. 2, theintroduction transport path Rt2 is formed by disposing multiple guidingmembers 46 a, 46 b, 56 that ensure the transport space for the sheet ofpaper 9 and guide the transport of the sheet of paper 9. Among these,the guiding member 56 is a guiding member for introduction provided atan introduction port of a housing 50 of the fixing device 5.

A dashed-dotted line VL illustrated in FIG. 2 and other figuresindicates an ideal transport path for the sheet of paper 9 in theintroduction transport path Rt2. The dashed-dotted line VL is an idealline obtained by connecting a point CP1 and a point CP2, the point CP1being an intersection point at which the nip part of the second transferposition TP2 intersects the line obtained by connecting a rotationalcenter C1 of the support roller 32 e of the intermediate transfer belt31 and a rotational center C2 of the roll-shaped second transfer memberof the second transfer device 35, the point CP2 being an intersectionpoint at which the nip part FN intersects the line obtained byconnecting a rotational center C3 of the rotational body 51 for heatingand a rotational center C4 of the rotational body 52 for pressurizing inthe fixing device 5.

In addition, in the image forming apparatus 1, as illustrated in FIG. 1,a discharge transport path Rt3 for transporting the sheet of paper 9after fixing completed to the discharge port 13 and discharging thesheet of paper 9 to the discharge storage 12 is provided between thefixing device 5 and the discharge port 13. The discharge transport pathRt3 is formed by disposing a pair of discharge rollers 47 in front ofthe discharge port 13, and a guiding member (not illustrated) thatensures the transport space for the sheet of paper 9 and guides thetransport of the sheet of paper 9.

The control unit 15 includes, for instance, an arithmetic processingdevice, memory element and device, an I/O device, and a control devicefor those devices.

As illustrated in FIG. 4, the control unit 15 includes a centralcontroller 151 that integrates and controls the entire operations of theimage forming apparatus 1; image forming controllers 153Y, 153M, 153C,153K that control the operations of the image forming devices 2 (Y, M,C, K) of the four colors (Y, M, C, K); an intermediate transfercontroller 154 that controls the operations of the intermediate transferdevice 3; a sheet transport controller 155 that controls the operationsof the sheet feeding device 4, the sheet feeding transport path Rt1, andthe discharge transport path Rt3; and a fixture controller 156 thatcontrols the operations of the fixing device 5. Among these, the centralcontroller 151 has a memory 152 including the above-mentioned memoryelement and device that store a control program for the entire controlof the image forming apparatus 1 and information such as data necessaryfor the control. The other controllers 153 to 156 also have respectivememories that store necessary control program and data.

As illustrated in FIG. 4, the control unit 15 is connected to acommunication unit 16 that exchanges information with an externalconnection device or the like by a desired communication unit, an imageprocessor 17 that performs necessary processing on image informationinputted to the image forming apparatus 1 from the external connectiondevice, and a detector 18 that detects an operation and a state withinthe image forming apparatus 1. The control unit 15 is configured toinput and output necessary information (signals) to and from thosetargets to be connected.

Furthermore, in the image forming apparatus 1, a non-transferred tonerimage NT, which is not transferred to the sheet of paper 9, is formed bythe image forming device 2.

The non-transferred toner image NT is formed as a toner image in apredetermined pattern on the photoreceptor drum 21 by each relevantimage forming device 2 (Y, M, C, K), then is first transferred to theintermediate transfer belt 31 of the intermediate transfer device 3under normal transfer conditions. Subsequently, the non-transferredtoner image NT is passed through the second transfer position TP2 underconditions which cause no transfer effect by the second transfer device35. Consequently, the non-transferred toner image NT does not come intocontact with the intermediate transfer belt 31 at the second transferposition TP2 and is not secondarily transferred to the sheet of paper 9.The non-transferred toner image NT which passes through the secondtransfer position TP2 is finally removed from the outer circumferentialsurface of the intermediate transfer belt 31 by the belt cleaning device36 of the intermediate transfer device 3.

Such non-transferred toner image NT includes, for instance, thefollowing images.

Specifically, the non-transferred toner image NT includes a patch imageNT1 for process control formed when image formation conditions(conditions necessary for image formation, such as a concentration, andpositioning) are adjusted, and a pattern image NT2 for registrationcontrol formed when misregistration of the position of a toner imageformed is checked or eliminated (see FIG. 7). For the patch image NT1for process control and the pattern image NT2 for registration controlwhich are formed in order to obtain the control information, asillustrated in FIGS. 2 and 3, image reading sensors 18A, 18B for readingthe patch image NT1 for process control and the pattern image NT2 forregistration control are each disposed at a predetermined position ofthe intermediate transfer belt 31. The image reading sensors 18A, 18B inthe first exemplary embodiment are each disposed at a position in frontof where the intermediate transfer belt 31 is supported by the supportroller 32 d.

In addition, the non-transferred toner image NT includes a toner bandimage NT3 which is formed to reduce the occurrence of crying noise andturn-up phenomenon of the plate-like cleaning member 36 b of the beltcleaning device 36. Furthermore, the non-transferred toner image NTincludes a discharge toner image NT4. When a predetermined amount ofimage including a low concentration toner image is (continuously)formed, the discharge toner image NT4 is formed to forcedly dischargedeteriorated toner in the developing devices 24 (Y, M, C, K) of theimage forming devices 2 by a predetermined amount.

In the image forming apparatus 1, as illustrated in FIG. 5, thenon-transferred toner image NT is configured to be formed in ranges Ha,Hb, Hc of the intermediate transfer belt 31, where the separationdevices 37 (37A, 37B) are not present.

In this configuration, in other words, for instance, the non-transferredtoner image NT is not formed in ranges Hd, He (see FIG. 5, FIG. 7) ofthe intermediate transfer belt 31, where the separation devices 37 (37A,37B) are present.

As illustrated in FIG. 5, the range Ha is an inward range between twoseparation devices 37A, 37B, when viewed across the width direction J ofthe intermediate transfer belt 31.

In contrast, the range Hb is a range on one end side (near side of theapparatus) between the separation device 37A on one side (near side ofthe apparatus) and a lateral end 31 a on one side of the intermediatetransfer belt 31. The range Hc is a range on the other end side (farside of the apparatus) between the separation device 37B on the otherside (far side of the apparatus) and a lateral end 31 b on the otherside of the intermediate transfer belt 31.

The symbol Hd in FIG. 5 indicates the range of the intermediate transferbelt 31, where the separation device 37A is present, and the symbol Heindicates the range of the intermediate transfer belt 31, where theseparation device 37B is present.

The ranges Ha, Hb, Hc of the intermediate transfer belt 31, where theseparation devices 37 (37A, 37B) are not present are set in thefollowing manner, for instance.

Specifically, as conceptually illustrated in FIG. 6, the ranges Ha, Hb,Hc which are divided by imaginary boundary lines (dashed-two dottedlines in FIG. 6) which pass through positions in the rotationaldirection B, the positions being away from a leading end 371 a of theseparation claw 371 of the separation device 37A by predetermineddistances L1, L2 in the width direction J, the leading end 371 a beingin contact with the outer circumferential surface of the intermediatetransfer belt 31. It is sufficient that the predetermined distances L1,L2 be effective lengths to prevent the toner of part of thenon-transferred toner image NT from adhering to the separation claw 371.For instance, the distances L1, L2 are 1 to 3 cm. It is sufficient thatthe distances L1, L2 be the same lengths, but may be different lengthsfrom each other. The distances L1, L2 are also set in the otherseparation device 37B from the same point of view.

As in the separation device 37A in the first exemplary embodiment, whenthe fixing frame 370 is present which indicates one range of theseparation device 37A, as illustrated in FIG. 6, the ranges Ha, Hb, Hccan be set as the ranges divided by imaginary boundary lines (dashed-twodotted lines in FIG. 6) which pass through positions in the rotationaldirection B, the positions being away from the fixing frame 370 bypredetermined distances L3, L4 in the width direction J. The distancesL3 and L4 are set at will from the same point of view for the case ofthe distances L1, L2. The distances L3, L4 are also set in the otherseparation device 37B from the same point of view.

The non-transferred toner image NT formed in the ranges Ha, Hb, Hc,where the separation devices 37 (37A, 37B) are not present, of theintermediate transfer belt 31 starts to be formed by each relevant imageforming device 2 (Y, M, C, K) at a predetermined time based on imageinformation which is stored in a relevant component related to thecontrol unit 15 in advance as patterns of positions for image formation.The relevant component includes, for instance, the memory 152 of thecentral processor 151, the memory of the four color image formingcontrollers 153, and the memory of the image processor 17.

The non-transferred toner image NT is not particularly restricted exceptthat the range for image formation is restricted. Thus, for thenon-transferred toner image NT, the conditions for concentration,formation timing, for instance, are not required to be changedparticularly, and conventional conditions may be applied. However, thenon-transferred toner image NT is not formed in the ranges Hd, He of theintermediate transfer belt 31, where the separation devices 37 (37A,37B) are present, thus it is possible to adjust a formation pattern of atoner image or a toner amount to supplement the non-formation of image.

FIG. 7 illustrates a specific example of the non-transferred toner imageNT which is formed in the ranges Ha, Hb, Hc of the intermediate transferbelt 31, where the separation devices 37 (37A, 37B) are not present.

For instance, the patch image NT1 for process control as thenon-transferred toner image NT is formed in a predetermined pattern inthe range Hc of the intermediate transfer belt 31 when control to adjustthe process conditions is to be performed.

The pattern image NT2 for registration control as the non-transferredtoner image NT is formed in a predetermined pattern in the range Hb ofthe intermediate transfer belt 31 when control to correctmisregistration is to be performed.

The toner band image NT3 as the non-transferred toner image NT is formedin a pattern divided into thirds to be distributed to the ranges Ha, Hb,Hc of the intermediate transfer belt 31 at a predetermined timing. It isdesirable that the toner band image NT3 be formed in all of the rangesHa, Hb, Hc from the point of view of eliminating a problem in the beltcleaning device 36 by supplying toner to the entire area of a leadingend 36 be of the plate-like cleaning member 36 b of the belt cleaningdevice 36.

At a desired timing after a low concentration image in a predeterminedamount is formed, the discharge toner image NT4 as the non-transferredtoner image NT is formed in a predetermined pattern in the range Ha ofthe intermediate transfer belt 31, for instance. Incidentally, thedischarge toner image NT4 may be formed in one or both of the ranges Hb,Hc in addition to the range Ha of the intermediate transfer belt 31.

For any type of the non-transferred toner image NT, formation thereofstarts in the following manner: an electrostatic latent image for thenon-transferred toner image NT is formed in a desired pattern on thephotoreceptor drum 21 of each relevant image forming device 2 (Y, M, C,K) by an exposure operation of the exposure device 23, then theelectrostatic latent image is formed as a toner image having apredetermined concentration by a developing operation of each relevantdeveloping device 24 (Y, M, C, K).

In this process, the electrostatic latent image for the non-transferredtoner image NT is formed in the area (see FIG. 6) of the photoreceptordrum 21, corresponding to the ranges Ha, Hb, Hc of the intermediatetransfer belt 31.

Subsequently, the non-transferred toner image NT formed on thephotoreceptor drum 21 in each relevant image forming device 2 (Y, M, C,K) is first transferred to the ranges Ha, Hb, Hc of the intermediatetransfer belt 31 of the intermediate transfer device 3 by the firsttransfer process of the first transfer device 25, then is transported bythe intermediate transfer belt 31 that rotates in the directionindicated by the arrow B, but is passed through the second transferposition TP2 without being secondarily transferred to the sheet of paper9 at the TP2.

In this process, in the second transfer device 35, the conditions areswitched to those that do not allow the non-transferred toner image NTon the intermediate transfer belt 31 to be transferred to the secondtransfer device 35. Incidentally, for the patch image NT1 for processcontrol and the pattern image NT2 for registration control of thenon-transferred toner image NT, the state of image formation is read bythe image reading sensors 18A, 18B. The information (signal) read by theimage reading sensors 18A, 18B is transmitted to the central controller151 in the control unit 15, and is used as the control information.

Sequentially, the non-transferred toner image NT, which has passedthrough the second transfer position TP2 of the intermediate transferdevice 3, passes through the area (the ranges Ha, Hb, Hc) of the outercircumferential surface of the intermediate transfer belt 31, where theseparation devices 37 disposed immediately after the second transferposition TP2 are not present, and is finally removed and collected fromthe outer circumferential surface of the intermediate transfer belt 31by the belt cleaning device 36.

In this process, the non-transferred toner image NT on the outercircumferential surface of the intermediate transfer belt 31 does notcome into contact with the leading end 371 a of the separation claw 371of each separation device 37, and passes through a position away fromthe leading end 371 a of the separation claw 371 by at least thedistances L1, L2.

Thus, in the image forming apparatus 1, when the non-transferred tonerimage NT is formed, as compared with when the non-transferred tonerimage NT is similarly formed also in the ranges Hd, He of theintermediate transfer belt 31, where the separation devices 37 (37A,37B) are present, toner of part of the non-transferred toner image NTformed in the ranges Ha, Hb, Hc of the intermediate transfer belt 31 isprevented from coming into contact with and adhering to the leading end371 a of the separation claw 371, and the toner is blocked or sometimesprevented from floating, scattering, and adhering to or accumulating ona portion 371 c (see FIG. 8), on the side where a separated sheet ofpaper 9 passes through, of the separation claw 371.

Consequently, in the image forming apparatus 1, for instance when animage is formed using the sheet of paper 9 of the type represented bythick paper or relatively firm paper, as illustrated in FIG. 8, after arear end 9 b of the sheet of paper 9 in the transport direction passesthrough the second transfer position TP2 (after a sandwich state at thesecond transfer position TP2 is released), even if the rear end 9 b maycome closer and come into contact with the leading end 371 a of theseparation claw 371, there is no possibility of occurring a problem suchthat toner adhering to or accumulating on the leading end 371 a of theseparation claw 371 and/or the portion 371 c on the side where the sheetof paper 9 passes through is transferred to the rear end 9 b. The symbol9 a in FIG. 8 indicates the leading end of the sheet of paper 9 in thetransport direction.

In contrast, as illustrated by the toner band image NTx3 and thedischarge toner image NTx4 in FIG. 15 as the non-transferred toner imageNT, when the non-transferred toner image NT is similarly formed also inthe ranges Hd, He of the intermediate transfer belt 31, where theseparation devices 37 (37A, 37B) are present, the following problemcaused by the separation devices 37 may occur. Here, “similarly formed”refers to formation under the same conditions, such as a concentrationfor image formation, as those applied to the non-transferred toner imageNT formed in the ranges Ha, Hb, Hc.

Specifically, in this case, as illustrated in FIG. 16A, toner of part ofthe toner band image NTx3 and the discharge toner image NTx4 comes intocontact with the leading end 371 a of the separation claw 371 in eachseparation device 37, and adheres to the leading end 371 a of theseparation claw 371 and/or the portion 371 c on the side where the sheetof paper 9 passes through, as adherence toner Tx.

Thus, as illustrated in FIG. 16B, when the rear end 9 b of the sheet ofpaper 9 at the time of image formation passes through the secondtransfer position TP2, then comes closer and comes into contact with theleading end 371 a of the separation claw 371, part or all of theadherence toner Tx adhering to or accumulating on the leading end 371 aof the separation claw 371 is transferred to the rear end 9 b of thesheet of paper 9, which becomes dirty, what is called sheet rear endedge stain may occur. Also, since the rear end 9 b of the sheet of paper9 comes into contact with the separation claw 371 and applies an impactthereto, part or all of the adherence toner Tx adhering to oraccumulating on the leading end 371 a may float or scatter, and istransferred to the printed surface (front surface or back surface) ofthe sheet of paper 9, what is called sheet printed surface stain mayoccur.

Incidentally, as illustrated by an elliptic dotted line frame in FIG.17, the sheet rear end edge stain becomes noticeable when multiplesheets of paper 9 are stacked. In contrast, as illustrated by atrapezoidal dotted line frame in FIG. 17, the sheet printed surfacestain is visually recognized regardless of the stacked state of thesheets of paper 9.

In this regard, with the image forming apparatus 1 according to thefirst exemplary embodiment, even when the non-transferred toner image NTis formed, the occurrence of the problem (the sheet rear end edge stain,the sheet printed surface stain) caused by the separation devices 37 asillustrated above is reduced.

Incidentally, with the image forming apparatus 1, even when it isdifficult to change the position of the separation devices 37 (37A, 37B)for some reasons, the occurrence of the problem caused by the separationdevices 37 is reduced by forming the non-transferred toner image NT.

Second Exemplary Embodiment

FIGS. 9 and 10 illustrate part of an image forming apparatus accordingto the second exemplary embodiment.

The image forming apparatus according to the second exemplary embodimenthas the same configuration as that of the image forming apparatus 1according to the first exemplary embodiment except that additionally, alow concentration non-transferred toner image LNT is formed as thenon-transferred toner image NT in the ranges Hd, He of the intermediatetransfer belt 31, where at least the separation devices 37 are present,the low concentration non-transferred toner image LNT being lower inconcentration than a normal non-transferred toner image NT which isformed in the ranges Ha, Hb, Hc of the intermediate transfer belt 31,where the separation devices 37 (37A, 37B) are not present.

First, in the image forming apparatus according to the first exemplaryembodiment, a normal non-transferred toner image NT is not formed in theranges Hd, He of the intermediate transfer belt 31, where the separationdevices 37 are present,

For this reason, the normal non-transferred toner image NT does notarrive at the portion, corresponding to the ranges Hd, He, of theleading end 36 be of the plate-like cleaning member 36 b of the beltcleaning device 36, as compared with the portion corresponding to theranges Ha, Hb, Hc, thus the amount of supplied toner is relatively lowaccordingly. As a consequence, in (the cleaning member 36 b of) the beltcleaning device 36, the problem (crying noise and turn-up phenomenon inthe cleaning member 36 b) may occur in the portion corresponding to theranges Hd, He.

In this regard, with the image forming apparatus according to the secondexemplary embodiment, in addition to the normal non-transferred tonerimage NT, the low concentration non-transferred toner image LNT isformed in the ranges Hd, He of the intermediate transfer belt 31, whereat least the separation devices 37 are present, thus as compared withwhen the low concentration non-transferred toner image LNT is notformed, the occurrence of the problem of the belt cleaning device 36 atthe portion of the intermediate transfer belt 31 corresponding to theranges Hd, He is reduced.

In this process, since the low concentration non-transferred toner imageLNT comes into contact with and passes through the separation claw 371of each separation device 37 (37A, 37B), the concentration of the lowconcentration non-transferred toner image LNT needs to be set low enoughso that toner of part of the low concentration non-transferred tonerimage LNT does not adhere to the separation claw 371.

Similarly to the case of the non-transferred toner image NT, the lowconcentration non-transferred toner image LNT starts to be formed byeach relevant image forming device 2 (Y, M, C, K) at a predeterminedtime based on image information which is stored in a relevant componentrelated to the control unit 15 in advance as patterns of positions forimage formation. The relevant component includes, for instance, thememory 152 of the central processor 151, the memory of the four colorimage forming controllers 153, and the memory of the image processor 17.

Next, as conceptually illustrated in FIG. 9, the image forming apparatusaccording to the second exemplary embodiment forms the low concentrationnon-transferred toner image LNT at a time different from the time forthe non-transferred toner image NT. FIG. 9 illustrates two configurationexamples as representatives when the low concentration non-transferredtoner image LNT is formed at a different time.

In one configuration example, when the toner band image NT3 is formed asthe normal non-transferred toner image NT, a toner band image LNT3 lowerin concentration than the toner band image NT3 is formed at a differenttime.

For the sake of convenience, FIG. 9 illustrates the case where the lowconcentration toner band image LNT3 is formed successively slightlyafter the normal toner band image NT3 is formed. However, the “formed ata different time” includes the case where the low concentration tonerband image LNT3 is singly formed at a time completely different from thetime when the normal toner band image NT3 is formed.

In the other configuration example, when the discharge toner image NT4is formed as the normal non-transferred toner image NT, a dischargetoner image LNT4 lower in concentration than the discharge toner imageNT4 is formed at a different time. Due to the situation that the normalnon-transferred toner image NT is a pattern which is formed only in therange Ha of the intermediate transfer belt 31, the low concentrationdischarge toner image LNT4 is formed in an area including the ranges Hb,Hc in addition to the ranges Hd, He.

Similarly to the case of the low concentration toner band image LNT3,for the sake of convenience, FIG. 9 illustrates the case where the lowconcentration discharge toner image LNT4 is formed successively slightlyafter the normal discharge toner image NT4 is formed. However, the“formed at a different time” includes the case where the lowconcentration discharge toner image LNT4 is singly formed at a timecompletely different from the time when the normal discharge toner imageNT4 is formed.

When the low concentration non-transferred toner image LNT is formed ata time different from the time for the normal non-transferred tonerimage NT in this manner, the time for forming the low concentrationnon-transferred toner image LNT can be set independently from the timefor forming the normal non-transferred toner image NT, as compared withwhen the low concentration non-transferred toner image LNT and thenormal non-transferred toner image NT are formed at the same time. Thus,it is possible to form the low concentration non-transferred toner imageLNT only when necessary.

Consequently, in the belt cleaning device 36, the occurrence of theproblem at the portion of the cleaning member 36 b corresponding to theranges Hd, He of the intermediate transfer belt 31 is reliably reduced.It is to be noted that the low concentration non-transferred toner imageLNT formed at a different time may be formed in one of the ranges Ha,Hb, Hc in addition to the ranges Hd, He.

In the image forming apparatus according to the second exemplaryembodiment, as conceptually illustrated in FIG. 10, the lowconcentration non-transferred toner image LNT and the normalnon-transferred toner image NT may be formed at the same time. FIG. 10illustrates two configuration examples as representatives when the twotoner images are formed at the same time.

In one configuration example, when the toner band image NT3 is formed asthe normal non-transferred toner image NT, the low concentration tonerband image LNT3 is formed synchronized with the time when the normaltoner band image NT3 is formed. The “formed synchronized with the time”indicates that at least the start time for forming the normal toner bandimage NT3 is the same as the start time for forming the lowconcentration toner band image LNT3.

In the other configuration example, when the discharge toner image NT4is formed as the normal non-transferred toner image NT, the lowconcentration discharge toner image LNT4 is formed synchronized with thetime when the normal discharge toner image NT4 is formed. Similarly tothe case of formation time of the low concentration toner band imageLNT3, the “formed synchronized with the time” in this case indicatesthat at least the start time for forming the normal discharge tonerimage NT4 is the same as the start time for forming the lowconcentration discharge toner image LNT4.

The normal discharge toner image NT4 illustrated in FIG. 10 is anexample where image formation is made in the range Ha excluding theranges Hb, Hc of the intermediate transfer belt 31. Due to thissituation, the low concentration discharge toner image LNT4 is formednot only in the ranges Hd, He of the intermediate transfer belt 31, butalso in the ranges Hb, Hc.

When the low concentration non-transferred toner image LNT and thenormal non-transferred toner image NT are formed at the same time inthis manner, the low concentration non-transferred toner image LNT isreliably formed synchronized with the time when the normalnon-transferred toner image NT is formed, as compared with when the lowconcentration non-transferred toner image LNT and the normalnon-transferred toner image NT are formed at different times, and thusthe number of singly forming the low concentration non-transferred tonerimage LNT independently from forming the normal non-transferred tonerimage NT can be reduced.

In this case also, in the belt cleaning device 36, the occurrence of theproblem at the portion of the cleaning member 36 b corresponding to theranges Hd, He of the intermediate transfer belt 31 is reliably reduced.In addition, the low concentration non-transferred toner image LNTillustrated in FIG. 10 is also formed in the ranges Hb, Hc of theintermediate transfer belt 31, thus the occurrence of the problem at theportion of the cleaning member 36 b corresponding to the ranges Hb, Hcof the intermediate transfer belt 31 is also reduced.

It is to be noted that in the image forming apparatus according to thesecond exemplary embodiment, a configuration in which the lowconcentration non-transferred toner image LNT and the normalnon-transferred toner image NT are formed at different times, and aconfiguration in which the low concentration non-transferred toner imageLNT and the normal non-transferred toner image NT are formed at the sametime may be combined.

In addition, as illustrated in FIGS. 9 and 10, the length of the lowconcentration non-transferred toner image LNT in the rotationaldirection B is longer than the length of the normal non-transferredtoner image NT. Consequently, it is possible to adjust the total amountof toner to be supplied to the portion of the cleaning member 36 b ofbelt cleaning device 36, corresponding at least to the ranges Hb, Hc bythe formation of the low concentration non-transferred toner image LNT.

However, it is also effective that the above-mentioned length of the lowconcentration non-transferred toner image LNT is set to be equal to orshorter than the length of the normal non-transferred toner image NT inconsideration of the importance of avoiding the adherence of toner tothe separation claw 371 of each separation device 37.

FIG. 11 illustrates a result of an experiment when the relationshipbetween the concentration of the low concentration non-transferred tonerimage LNT and occurrence of the rear end stain of the sheet of paper 9is investigated using the image forming apparatus.

In this experiment, an image of black toner with a length of 600 mm isassumed to be formed as the normal non-transferred toner image NT, and acorresponding non-transferred toner image LNT having multiple types ofexperimental concentrations indicated by plotting in FIG. 11 is formedonce in the ranges Hd, He at the same time when the normalnon-transferred toner image NT is formed. Subsequently, when the sheetof paper 9 is passed through the second transfer position TP2, it isinvestigated whether or not toner is adhering to the rear end 9 b of thesheet of paper 9 and the rear end edge stain has occurred.

In this process, the concentration of the low concentrationnon-transferred toner image LNT is measured using a measuring instrument(spectral densitometer: X-Rite 962). The non-transferred toner imagesLNT having various experimental concentrations are formed based on theinformation on the concentration measured by the measuring instrument.

The occurrence of the rear end edge stain is evaluated by the followingcriteria, and the result is shown in FIG. 11 as an evaluation grade. Theacceptable level is lower than or equal to G1.

Grade G0: no occurrence

Grade G1: occurrence of adherence with a very slight amount which isdifficult to visually recognize even when multiple sheets are stacked

Grade G2: occurrence of adherence with a slight amount which can bevisually recognized when multiple sheets are stacked

Grade G3: occurrence of adherence with a level which can be easilyrecognized by naked eyes

From the result shown in FIG. 11, it is seen that when the lowconcentration non-transferred toner image LNT is formed with aconcentration of 0.4 or lower as compared with a concentration of 0.8 orhigher, the rear end stain does not occur or an acceptable level isachieved. Incidentally, the normal non-transferred toner image NT atthis point is formed with a concentration in a range from 0.8 to 1.3.

With this result, from the point of view of reducing or preventing theoccurrence of rear end edge stain, it is preferable that theconcentration of the low concentration non-transferred toner image LNTbe 50% or lower of the normal non-transferred toner image NT. Inaddition, from point of view of reliably preventing the occurrence ofrear end edge stain, it is more preferable that the concentration of thelow concentration non-transferred toner image LNT be 0.2 or lower, andit is sufficient that the concentration of the low concentrationnon-transferred toner image LNT be equal to or lower than theconcentration of the normal non-transferred toner image NT.

Third Exemplary Embodiment

FIG. 12 illustrates part of an image forming apparatus according to athird exemplary embodiment.

The image forming apparatus according to the third exemplary embodimenthas the same configuration as that of the image forming apparatusaccording to the first and second exemplary embodiments except that theseparation devices 37 (37A, 37B) are changed to separation devices 37(37C, 37D) having a different configuration.

As illustrated in FIGS. 12, 13A, and 13B, the separation devices 37(37C, 37D) includes the separation claws 371 of the separation devices37A, 37B in the first and second exemplary embodiments, and a covercomponent 375 which is disposed to cover the portion 371 c of theseparation claws 371 on the side where a separated sheet of paper 9passes through. The symbol 370 a in FIGS. 13A and 13B indicates a shaftreceiver which is provided in the fixing frame 370 to rotatably supporta support shaft 372 of the separation claws 371. The symbol 38 bindicates a mounting notch provided in the mounting plate 38 forallowing the shaft receiver 370 a of the fixing frame 370 to be fittedin.

As illustrated in FIG. 13B, the cover component 375 includes aplate-like main body section 376 that actually covers the portion 371 cof the separation claw 371 on the side where the sheet of paper 9 passesthrough, and a mounting section 377 for mounting the main body section376 on the fixing frame 370 in combination with the separation claws371.

The main body section 376 is a substantially rectangular plate-likesection with a size covering the entire portion 371 c of the separationclaw 371. As illustrated in FIG. 14, the main body section 376 has ashape bent upward so that a leading end 376 a, which comes closer to theouter circumferential surface of the intermediate transfer belt 31, isdisplaced and away from the outer circumferential surface by a desireddistance.

The mounting section 377 is a section having a shape which extends fromthe rear end and one lateral end downward on the rear side of the mainbody section 376. The mounting section 377 is provided with a shaftreceiving hole 377 a into which one support shaft 372 of the separationclaw 371 is fitted and penetrates.

The separation devices 37 (37C, 37D) are assembled in the followingmanner: the cover component 375 achieves a state of being integratedwith the separation claw 371 by fitting one support shaft 372 of theseparation claw 371 into the shaft receiving hole 377 a of the mountingsection 377 for penetration, then the support shaft 372 of theseparation claw 371 is mounted on the shaft receiver 370 a of the fixingframe 370, and the elastic member 373 such as a coil spring is attachedto the separation claw 371.

In the image forming apparatus according to the third exemplaryembodiment, the separation devices 37 (37C, 37D) including the covercomponent 375 are applied to the intermediate transfer device 3. Thus,at the time of the operation of forming a normal image comprised of atoner image to be transferred to the sheet of paper 9, even when thesecond transfer is not performed and the intermediate transfer belt 31with remaining transfer residual toner passes through the separationdevices 37C, 37D, or the low concentration non-transferred toner imageLNT is formed and passes through the separation devices 37C, 37D, toneris unlikely to adhere to the portion 371 c of the separation claw 371 onthe side where the sheet of paper 9 passes through because theseparation claw 371 is covered by the cover component 375.

In the image forming apparatus, as illustrated in FIG. 14, even when therear end 9 b of the sheet of paper 9, which has passed through thesecond transfer position TP2, comes closer to the separation devices37C, 37D, and passes therethrough in a contact state, the rear end 9 bof the sheet of paper 9 does not directly come into contact with theleading end 371 a of the separation claw 371 although the rear end 9 bmay come into contact with the cover component 375.

Even when toner adheres to and accumulates on the leading end 371 a ofthe separation claw 371, and the rear end 9 b of the sheet of paper 9passes through the separation devices 37C, 37D in a contact state,direct contact of the rear end 9 b of the sheet of paper 9 with theleading end 371 a of the separation claw 371 is prevented, andadditionally, even when toner accumulating on the portion 371 c of theseparation claw 371 is scattered due to an impact of the contact,movement of the toner is prevented by the cover component 375, andtransfer of the toner to the rear end printed surface of the sheet ofpaper 9 is reduced.

Consequently, rear end stain of the sheet of paper 9 is unlikely tooccur in the image forming apparatus.

Thus, in the image forming apparatus, as compared with when theseparation device is not configured by the separation claw 371 and thecover component 375, it is possible to prevent toner from adhering tothe portion 371 c of the separation claw 371 on the side where the sheetof paper 9 passes through, and to reduce the occurrence of rear endstain of the sheet of paper 9.

Other Modifications

The disclosure is not limited to the content illustrated in the first tothird exemplary embodiments, and includes, for instance, themodifications shown below.

The number of separations devices 37 installed is not limited to two,and may be greater than two or one.

The image forming apparatus 1 is not limited to an intermediate transferimage forming apparatus including the intermediate transfer device 3illustrated in the first to third exemplary embodiments, and may be adirect transfer image forming apparatus that directly transfers a tonerimage formed on a photoreceptor such as a photoreceptor drum to a sheetof paper.

The direct transfer image forming apparatus also includes, for instance,a contact separation device that separates a sheet of paper, in thephotoreceptor drum 21 which is an example of the image carrying unit,and when a non-transferred toner image NT is formed in the photoreceptordrum 21, the non-transferred toner image NT may be formed in a range ofthe photoreceptor drum 21 where the separation device is not present. Inthis image forming apparatus, a low concentration non-transferred tonerimage LNT may be formed in a range of the photoreceptor drum 21 where atleast a separation device is present.

In addition, the disclosure is similarly applicable to a direct transferimage forming apparatus that transports a sheet of paper to a transferposition of a photoreceptor by a transfer transport belt device, andperforms transfer.

The foregoing description of the exemplary embodiments of the presentdisclosure has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical applications, therebyenabling others skilled in the art to understand the disclosure forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of thedisclosure be defined by the following claims and their equivalents.

What is claimed is:
 1. An image forming apparatus comprising: an imagecarrying unit that carries an image to be transferred to a sheet whichis brought into contact with the image carrying unit and passed through;a separation unit that separates the sheet from the image carrying unit;and a removal unit that comes into contact with the image carrying unit,and removes toner remaining after the sheet passes the separation unit,wherein a non-transferred toner image that is not transferred to thesheet is formed in a range, where the separation unit is not present, ofthe image carrying unit, wherein a low concentration non-transferredtoner image is formed in a range, where at least the separation unit ispresent, of the image carrying unit, the low concentrationnon-transferred toner image being lower in concentration than a normalnon-transferred toner image formed in the range where the separationunit is not present.
 2. The image forming apparatus according to claim1, wherein the low concentration non-transferred toner image and thenormal non-transferred toner image are formed at different times.
 3. Theimage forming apparatus according to claim 2, wherein the lowconcentration non-transferred toner image and the normal non-transferredtoner image are formed at a same time.
 4. The image forming apparatusaccording to claim 3, wherein the low concentration non-transferredtoner image is formed with a low concentration lower than or equal to50% of a concentration of the normal non-transferred toner image.
 5. Theimage forming apparatus according to claim 4, wherein the separationunit includes a separation claw that separates the sheet, and a covercomponent that is disposed to cover a portion of the separation claw ona side where the sheet passes.
 6. The image forming apparatus accordingto claim 3, wherein the separation unit includes a separation claw thatseparates the sheet, and a cover component that is disposed to cover aportion of the separation claw on a side where the sheet passes.
 7. Theimage forming apparatus according to claim 2, wherein the lowconcentration non-transferred toner image is formed with a lowconcentration lower than or equal to 50% of a concentration of thenormal non-transferred toner image.
 8. The image forming apparatusaccording to claim 7, wherein the separation unit includes a separationclaw that separates the sheet, and a cover component that is disposed tocover a portion of the separation claw on a side where the sheet passes.9. The image forming apparatus according to claim 2, wherein theseparation unit includes a separation claw that separates the sheet, anda cover component that is disposed to cover a portion of the separationclaw on a side where the sheet passes.
 10. The image forming apparatusaccording to claim 1, wherein the low concentration non-transferredtoner image and the normal non-transferred toner image are formed at asame time.
 11. The image forming apparatus according to claim 10,wherein the low concentration non-transferred toner image is formed witha low concentration lower than or equal to 50% of a concentration of thenormal non-transferred toner image.
 12. The image forming apparatusaccording to claim 11, wherein the separation unit includes a separationclaw that separates the sheet, and a cover component that is disposed tocover a portion of the separation claw on a side where the sheet passes.13. The image forming apparatus according to claim 10, wherein theseparation unit includes a separation claw that separates the sheet, anda cover component that is disposed to cover a portion of the separationclaw on a side where the sheet passes.
 14. The image forming apparatusaccording to claim 1, wherein the low concentration non-transferredtoner image is formed with a low concentration lower than or equal to50% of a concentration of the normal non-transferred toner image. 15.The image forming apparatus according to claim 14, wherein theseparation unit includes a separation claw that separates the sheet, anda cover component that is disposed to cover a portion of the separationclaw on a side where the sheet passes.
 16. The image forming apparatusaccording to claim 1, wherein the separation unit includes a separationclaw that separates the sheet, and a cover component that is disposed tocover a portion of the separation claw on a side where the sheet passes.17. The image forming apparatus according to claim 1, wherein theseparation unit includes a separation claw that separates the sheet, anda cover component that is disposed to cover a portion of the separationclaw on a side where the sheet passes.
 18. An image forming apparatuscomprising: image carrying means for carrying an image to be transferredto a sheet which is brought into contact with the image carrying meansand passed through; separation means for separating the sheet from theimage carrying means; and removal means, coming into contact with theimage carrying means, for removing toner remaining after the sheetpasses the separation means, wherein a non-transferred toner image thatis not transferred to the sheet is formed in a range, where theseparation means is not present, of the image carrying means, andwherein a low concentration non-transferred toner image is formed in arange, where at least the separation means is present, of the imagecarrying means, the low concentration non-transferred toner image beinglower in concentration than a normal non-transferred toner image formedin the range where the separation means is not present.